This invention relates to an improved apparatus for production of synthetic multifilamentary yarns having uniform quality from high molecular weight linear polymers, in particular polyamides and polyesters, according to an improved melt spinning process.
An important area of use of such synthetic multifilamentary yarns is the production of tire cord. A number of high polymers are well suited for this utility, especially polyesters and polyamides; however, in the following description reference will be made particularly to filaments of polyethylene terephthalate.
Since tire cord and the structures formed from it are among the essential construction elements for the safety and useful life of a tire, high quality requirements are naturally placed on such endless filaments. In view of the alternating stretching and compression stresses which tires experience in operation, a necessary precondition for the use of synthetic multifilamentary yarns for tire cord is an adequate fatigue resistance of the filaments. For optimum results, it is critical that the individual filaments be substantially uniform. Accordingly, it is common practice to determine the coefficient of variation of the evenness of the yarn (U %) using an Uster evenness tester as manufactured by the Zellweger Company of Uster, Switzerland, and described in "Handbook of Textile Testing and Quality Control" by E. Groover and D. S. Hamby.
The production of polyester yarns useful for tire, textile and industrial purposes is well known. In many of the prior art methods, the spinning and drawing and twisting of the filaments are separately carried out. However, several processes have been developed which involve conditions of continuously spinning and drawing filaments.
U.S. Pat. No. 3,433,008 to T. B. Gage discloses production of a bulked yarn by a process comprising applying a finish of an ester of polyethylene glycol of molecular weight between 150 and 600 and an aliphatic carboxylic acid to continuous melt spun filaments before the filaments are drawn. The filaments are then drawn and bulked in a turbulent fluid jet to give the bulked yarn.
U.S. Pat. No. 3,511,677 to A. J. Strohmaier et al. discloses preparation of a sized zero-twist synthetic fiber yarn by a process comprising applying a coating of a volatile medium containing a thermoplastic filmforming polymeric material to an undrawn yarn, drawing the yarn while wet with the volatile medium and then heating the drawn yarn to dry the coating before winding the yarn on a package.
U.S. Pat. No. 3,793,425 to R. J. Arrowsmith discloses a process for pretreating polyester filamentary material for subsequent rubber adhesion, the process comprising extruding a polyester filamentary material capable of being drawn and before the extrudate is fully drawn, coating with a composition containing an epoxy resin.
More recently, it has been suggested that a high strength polyester fiber can be produced by melt-spinning a polyester polymer under conditions of substantially simultaneous spinning and drawing wherein prior to said drawing the filaments of the fiber are lubricated by surface contact with a lube roll surface of not less than about 90 RMS. However, in commercial operation of said process at high throughput rates of 50 pounds per hour or greater through the spinneret, serious problems have been encountered due to "flicking" of filaments from the main yarn bundle above the lube roll, which flicking results in production of yarn of relatively poor quality. "Flicking" has been particularly troublesome in so-called double-end melt spinning of synthetic fibers, i.e., using one spin pot to feed both sides of a "split" spinneret. Accordingly, research has been continued in an effort to solve these deficiencies.
The term "RMS," which is short for root-mean-square, is an arbitrary measurement of surface texture and is described in detail in the publication, Surface Texture (ASA B 46.1 - 1962), The American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, N.Y. 17, New York, page 16 (1962). Such measurement is utilized throughout this invention disclosure unless otherwise stated.
The term "flicking" is conventionally applied and is used herein to mean a momentary slackness of a filament in the undrawn yarn above the lube zone. The slack filament bows out of phase from the main bundle, thus "flicking". It is known that excessive "flicking" normally causes production of yarn of relatively low quality having an excessive number of defects such as missing filaments, filament breaks and loops.